A book from 1985 that makes many books discussed here on Hacker News seem obsolete ("Four steps to the epiphany", etc.).
Drucker discusses 7 sources for finding the right idea, entrepreneurial management and startup strategies.
I was really suprised how good this book was: Very insightful and fun to read.
Price was 1,93 an Amazon Germany.
Bottom line: the best book an entrepreneurship I ever read.